Masonry Magazine February 1977 Page. 13
FIGURE 2.
CONCAVE
VEE
BEADED
WEATHERED
FLUSH
RAKED
STRUCK
EXTRUDED
Mortar Joints Suitable for Weathertight Concrete Masonry Construction
Mortar Joints Not Suitable for Weathertight Exterior Construction
maximum absorption of 10 pounds per cubic foot of concrete.
Mortar-The mortar properties required for weathertight concrete masonry construction are: (1) Workability, (2) Water retentivity, (3) Strength, (4) Adhesion, and (5) Durability. These properties may be obtained in mortars that comply with:
ASTM C 270 for Mortar for Nonreinforced Masonry
ASTM C 476 for Mortar for Reinforced Masonry
As with concrete masonry units, precise selection of mortar type will depend upon geographic area and the desired exterior surface treatment. If the wall surface is to be painted with an opaque protective waterproof coating, the mortar for nonreinforced masonry construction should comply with either grade N, S, or M of ASTM C 270, the exact choice depending upon structural loading rather than exposure. If the nonreinforced masonry is to be left unpainted or coated with a clear water repellant, that is, customized concrete masonry, then only type S or type M of ASTM C 270 should be employed. For reinforced masonry construction either type PM or type PL is satisfactory for both painted and unpainted situations.
Opaque Paint Coatings-Numerous waterproof coatings are available for the construction of weathertight concrete masonry walls. Generally these systems are two separate coats consisting of: (1) a fill coat to level out and fill the surface pores of the masonry, followed by (2) a finish decorative waterproofing coat. Repainting is, in most all cases, the finish coat only. The most common opaque paints are: (1) a latex base, (2) a portland cement base, or (3) a combination latex-portland cement base. Latex emulsions are: (1) polyvinyl acetates, (2) acrylics, and (3) styrene-butadienes. Table 1 lists some of the more important characteristics of these opaque coatings. Properly applied, they can be relied on to give a satisfactory weathertight concrete masonry wall for up to 8 or 10 years in most geographic areas.
Clear Coatings-Concrete masonry used as an architectural facing (Customized Concrete Masonry) is usually coated with a clear water repellant so as to retain its original unpainted appearance. As a class, the clear materials tend to be less effective than opaque coatings because they must have a lower content of solids (30-35 percent or less) to avoid forming a glossy film on the masonry surface. They are accordingly called "Water Repellants" instead of "Waterproof Coatings." To be successful, the clear water repellants must be used with masonry having a dense surface free of large pores or voids, that is, masonry that does not require a fill coat.
A good clear water repellant coating should:
Have good storage life and application characteristics.
Not change the appearance of the masonry.
Produce a surface that is resistant to rain penetration.
Be of a breathing type so that water vapor can travel through it to prevent condensation within the wall.
Resist efflorescence.
Be durable and resist the accumulation of air-borne contamination on the wall.
Workmanship
Workmanship applies not only to the care and technique with which concrete masonry is laid, but also to certain elements in the design which depend upon good workmanship for proper execution. Workmanship can and does greatly influence the weathertightness of a concrete masonry wall. In fact, studies have consistently shown that workmanship is the single most important factor affecting rain resistance. Close cooperation between the mason and designer is necessary if the weathertight details drawn in the architect's office are to become a reality in the field.
depth of structure
high parapet 15"
HIGH PARAPET
low parapet
15" max
LOW PARAPET
Drip Ledges on Both Sides
thru wall flashing
cap flashing
spandrel flashing
thru wall flashing
cap flashing
FIGURE 3. Parapet Details (High and Low)